1. Field of the Invention:
The present invention generally relates to the production of an antigen specific to non-A non-B hepatitis by recombinant DNA technology. More particularly, it relates to a DNA fragment coding for an antigen specifically occurring in a host affected with non-A non-B hepatitis, an expression vector containing such a DNA fragment, a host transformed with such an expression vector, as well as a process for producing said antigen specific to non-A non-B hepatitis by culturing such a transformant.
2. Description of the Prior Art:
Among viral hepatitises, the viral entities of hepatitis type A and type B have been found and, accordingly, it has now become possible to diagnose such diseases by immunological methods.
Still another type of hepatitis different from the types A and B, which is called non-A non-B type hepatitis, is said to be over 90% of post-transfusion hepatitis: refer to NIPPON RINSHO (Japan Clinic), 35, 2724 (1977): J. Biol. Med., 49, 243 (1976). The pathogenic virus of the non-A non-B type hepatitis, however, has not yet been identified. Only one fact which has already been established is potential infection of human hepatitis type non-A non-B virus to chimpanzee: refer to Lancet I, 459 (1978) ibid., 463 (1978).
Many workers have done various investigations for searching an antigen-antibody system related to the non-A non-B hepatitis by using mainly sera from patients affected with the disease; nevertheless, no definite system has been found. Under these circumstances, the diagnosis of non-A non-B hepatitis should inevitably be effected by so-called exclusion diagnosis: that is, whether or not the hepatitis of a patient is type A or type B or other hepatitis due to a virus known to cause hepatopathy, for example, CMV, HSV, EBV, etc., is first determined; and if not, the patient's hepatitis is diagnosed as non-A non-B type. Thus, such a diagnosis of non-A non-B hepatitis will require much time and labor.
An antigenic protein specific to non-A non-B hepatitis and useful for the direct diagnoses of the hepatitis has been purified from human and chimpanzee hepatocytes affected with non-A non-B hepatitis, and a monoclonal antibody specific to the antigen and useful for the treatment of the non-A non-B hepatitis has also been proposed: refer to Japanese Patent Application Laying-open (KOKAI) Nos. 176856/86 and 56196/86.
A large amount of such an antigenic protein specific to non-A non-B hepatitis should be required when such a protein is to be employed, for example, as a diagnostic agent. However, it is not always appropriate to purify such a large amount of the antigenic protein from chimpanzee hepatocytes affected with non-A non-B hepatitis.
On the other hand, in order to detect a gene coding for a specific antigen of non-A non-B hepatitis by nucleic acid hybridization and, further, to produce such an antigen specific to non-A non-B hepatitis by the recombinant DNA technology, it is essential to obtain a gene fragment coding for the antigenic protein specific to the non-A non-B hepatitis.